DTC P2520 or P2521. Saturn VUE

For 1990-2009 cars only

Makes 🢒 Saturn 🢒 2007 🢒 VUE - FWD 🢒 Diagnostic Navigation 🢒 Vehicle Diagnostic Information 🢒 DTC P2520 or P2521

Diagnostic Instructions

•	Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.

•	Review Strategy Based Diagnosis for an overview of the diagnostic approach.

•	Diagnostic Procedure Instructions provides an overview of each diagnostic category.

DTC Descriptors

DTC P2520: Air Conditioning (A/C) Request Circuit Low Voltage

DTC P2521: Air Conditioning (A/C) Request Circuit High Voltage

Diagnostic Fault Information

Circuit	Short to Ground	Open/High Resistance	Short to Voltage	Signal Performance
A/C Request Circuit	P2520	P2520	P2521	--

Ignition voltage is supplied directly to the A/C compressor clutch relay. The HVAC control module controls the a/c request circuit by grounding the A/C request circuit via an internal solid state device called a driver. The primary function of the driver is to supply the ground for the component being controlled. The driver has a fault line which is monitored by the engine control module (ECM). When the HVAC control module is commanding a component ON, the voltage of the a/c request circuit should be near 0 volts. When the HVAC control module is commanding the request circuit to a component OFF, the voltage potential of the circuit should be near battery voltage. If the fault detection circuit senses a voltage other than what is expected, these DTCs will set. There are three states the HVAC Control module can communicate to the ECM. These states are: A/C off, Normal A/C on, and Economy A/C on. The request is communicated from the HVAC Control Module to the ECM via a Pulse-Width Modulated signal on the A/C request circuit.

The ECM will monitor the request circuit for the following:

•	A short to ground

•	A short to voltage

•	An open circuit

When the ECM detects any of the above malfunctions, this DTC is set and the affected driver is disabled.

Conditions for Running the DTC

•	The engine is ON.

•	The ignition voltage is between 8.7-16 volts.

•	The engine speed is more than 80 RPM.

•	The HVAC control module driver transitions from ON to OFF or from OFF to ON.

Conditions for Setting the DTC

P2520

•	The ECM detects a short to ground on the A/C request circuit of the HVAC control module.

•	The ECM detects the A/C request signal circuit has a PWM cycle of 0-10 percent.

P2521

•	The ECM detects a short to voltage on the A/C request circuit of the HVAC control module.

•	The ECM detects the A/C request signal circuit has a PWM cycle of 90-100 percent.

Action Taken When the DTC Sets

•	The ECM will not illuminate the malfunction indicator lamp (MIL).

•	The ECM will store conditions which were present when the DTC set as Failure Records data only. This information will not be stored as Freeze Frame data.

•	A/C compressor is disabled.

Conditions for Clearing the DTC

•	A History DTC clears after 100 consecutive warm-up cycles have occurred without a malfunction monitored by the ECM.

•	The DTC can be cleared with a scan tool.

Diagnostic Aids

Important: Be sure to verify that the ECM engine grounds are secure and clean.

If DTC P2520, P2521 cannot be duplicated, reviewing the Failure Records vehicle millage since the diagnostic test last failed may help determine how often the condition that caused the DTC to set occurs. This may assist in diagnosing the condition.

If the condition is not present, refer to Testing for Intermittent Conditions and Poor Connections .

Reference Information

Schematic Reference

HVAC Schematics

Connector End View

HVAC Connector End Views

Description and Operation

•	Air Delivery Description and Operation

•	Air Temperature Description and Operation

Electrical Information Reference

•	Circuit Testing

•	Connector Repairs

•	Testing for Intermittent Conditions and Poor Connections

•	Wiring Repairs

Scan Tool Reference

•	Scan Tool Output Controls

•	Scan Tool Data List

•	Scan Tool Data Definitions

Circuit System Verification

Ignition ON, observe the scan tool A/C request parameter while pressing the A/C request switch of the HVAC control head. The reading should change between Yes and No A/C request value.

Circuit System Testing

Ignition OFF, disconnect the HVAC harness connector at the A/C switch.
Test for less than 1.0 ohm of resistance between the HVAC control module ground circuit terminal C1 pin 12 and ground.

⇒	If greater than the specified range, test the ground circuit for an open/high resistance.

Ignition ON, verify the scan tool ECM A/C request parameter is No or open.

⇒	If not the specified value, test the A/C request signal circuit terminal HVAC control module terminal C1 pin 8 for a short to ground. If the circuit tests normal, replace the HVAC control module.

Install a 3A fused jumper wire between the signal circuit terminal C1 pin 8 and the ground circuit terminal C1 pin 12. Verify the scan tool ECM A/C request switch parameter is YES or closed.

⇒	If not the specified value, test the A/C request signal circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the HVAC control module.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the repair.

Control Module References for HVAC replacement, setup, and programming